Please tell me is this possible:
If a user downloads a PDF file and opens it, and if the user is connected to Internet (when he opens a PDF file) then this particular PDF file should check if a new version or an update is available for this file (it should check from the original source from where it was created).
There are some workarounds to do the same thing with JavaScript, but it's not as reliable, and you wouldn't be able to force the user to update.